1. Field of the Invention
This invention relates to a damper apparatus for absorbing a sudden torque fluctuation in a torque converter with a lock-up mechanism in an automatic transmission for a vehicle, and more particularly to a damper apparatus in which the angle of torsion can be secured greatly by a simple construction and the life of a spring is improved.
2. Related Background Art
Generally, a torque converter transmits power through a fluid and therefore can realize smooth running, although it suffers from the disadvantage that fuel consumption is increased by the energy loss due to the slip of the fluid. In order to solve this, the latest torque converters are provided with a lock-up mechanism.
The lock-up mechanism is a mechanism which comprises a direct-coupled clutch (lock-up clutch) having a frictional surface and in which, when the speed of a vehicle reaches a predetermined speed or higher, the flow of the fluid in the torque converter automatically changes and urges the frictional surface of the piston of the direct-coupled clutch against the front cover of the torque converter to thereby directly couple an engine and drive wheels together. Thereby the influence of the slip of the fluid is eliminated and an improvement in fuel consumption can be achieved.
In such a torque converter, a sudden torque fluctuation occurs when the piston (lock-up piston) of the direct-coupled clutch is displaced between the joined state and the liberated state thereof with respect to the front cover of the torque converter. In order to absorb this torque fluctuation, there is provided a damper apparatus comprising a plurality of springs.
Usually, a damper apparatus in which springs are disposed on the inner and outer peripheries and are serially operated is exposed to the sudden torque fluctuations of these springs and an excessively great change in stress each time the direct-coupled clutch is connected and disconnected. Therefore, it has often been the case that the service life is reduced.
Heretofore, in order to prevent an excessively great torque from being applied to the springs, provision has been made of means for limiting the stroke of the springs. For example, in U.S. Pat. No. 5,246,399, a ring member is interposed in the intermediate portion of the damper apparatus to limit the angles of the inner and outer peripheral springs.
Also, in Japanese Patent Application Laid-Open No. 3-194247, the angle of the outer peripheral spring is limited by a cut-away portion provided on the outer side of an outer peripheral plate and the angle of the inner peripheral spring is limited by an inner side plate and the spacer of a rivet.
In the above-described prior-art damper apparatuses, however, the use of the ring member or the spacer of the rivet leads to an increased number of parts. Also, the width dimension of the rivet portion becomes great and there occurs interference friction resulting from increased weight or axial cumulative dimension, and it is necessary to make the dimensional accuracy of materials very precise in order to prevent backlash. Further, it is necessary to apply expensive heat treatment to the angle limiting portion in order to prevent abrasion due to vibration in a rotational direction.